High power ultraviolet (UV) light has known uses in various fields including, without limitation curing certain coatings, other resin-type materials and adhesives, and disinfecting medical devices and fluids such as, for example, water.
Known UV light sources include mercury vapor lamps, which generate continuous light, and pulse or flash-type sources, which typically generate UV light pulses by employing, for example, inert flash tubes.
Commercially available pulse UV sources can generate power levels of, for example, 1,000 watts-per-centimeter squared (w/cm2) peak power. Such power levels, for example, provide penetration through transparent protective layers covering a UV-curable material, with sufficient power for relatively quick curing of the material. An example is UV curing of layers of Blu-ray discs, comprising a transparent protective layer approximately 100 μm thick covering a UV-curable layer, which is formulated to absorb and be curable by light of a wavelength of approximately 180-600 nm.
Related art UV sources and related systems, however, have shortcomings. Mercury vapor and other continuous-type UV sources are inherently inefficient in terms of electrical power consumed versus UV light power generated. The inefficiency is due to much of the electrical power being generated as heat, or as light frequencies outside of the desired UV spectrum.
Pulse-type UV light sources are generally more efficient, in terms of UV power radiated compared to electrical power consumed than continuous-type UV sources. However, current methods and devices for measuring the radiated UV pulse power are relatively expensive, overly large, or not sufficiently accurate, particularly for the increasingly narrow UV pulse widths that are being used. One less expensive method and device for measuring UV pulse power employs “integrate and reset” method which connects an analog integrator to the photo-detector output and integrates that output over a time window spanning multiple UV pulses. At the end of the time window the integrator is sampled by an A/D converter and then discharged or reset. The A/D sample is the total accumulated energy of all of the UV pulses received by the photodetector over the time window. After the reset, the integrator integrates another sequence of multiple pulses, over another time window. At the end of the window, the integrator is sampled again, reset and the cycle repeats. The width of the time window is such that the integrator does not saturate.
One shortcoming of the integrate-and-reset device is that it measures only an accumulated energy of multiple pulses over a given time window. It does not provide measurement of individual pulse energy. Another shortcoming of the integrate-and-reset device is the finite range of the integrator, which necessitates setting the sample-and-reset window short enough so that, at least statistically, the accumulated energy of the UV pulses received over the window does not saturate the integrator. Still another shortcoming of the integrate-and-reset device is that stable integrators are often difficult to implement. Another shortcoming is error caused by leakage or bleed-off of the integrator over the span of the integration window.